<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
  p {
    color: blue;
  }
  /* .container:10  */
  .container p {
    color: red;
  }
  /* #:100 p:1 */
  #main p {
    color: green;
  }
  </style>
</head>
<body>
  <div id="main" class="container">
    <p>这是一个段落</p>
  </div>
</body>
</html>